The invention relates to a precisely movable mirror mount and, more particularly, to a mirror mount for use in a visual field tester.
Some people have impaired visual fields. These people cannot see at all or as well at certain solid angles from the visual axis of at least one of their eyes as can people with normal vision. This condition can, for example, arise from a damaged or imperfectly formed retina.
It is sometimes desirable to be able to determine the shape and extent of such visual field impairment for, for example, ascertaining changes in the condition through successive examinations to assess a treatment for the condition. Devices for testing visual field impairments are therefore available.
One type of visual field tester which is often referred to as a Goldman-type tester has a screen on which a light spot is projected in various positions relative to the visual axis of the eye being examined. The patient's ability to see the spot in the various positions relative to his visual axis which is fixed by looking at a fixation target, and the relative intensity of the light spot which can be seen can then be plotted to indicate the shape and extent of the patient's visual field impairment. In the Goldman-type device, a pantograph-like, mechanical arm arrangement links a device for projecting the light spot onto the screen to a handle for controlling the aim of the spot projection. The projector is positioned in front of the patient so as to be able to project the light spot to all portions of the screen, although sufficiently adjacent the patient as not to block the patient's view of the screen, and the pantograph-like arm arrangement extends to the other side of the screen so that the operator can observe the patient to check the patient's fixation of the optical axis of the eye being examined on the fixation target. This arrangement, although convenient for operation, places the entire pantograph-like arm arrangement adjacent and in front of the patient to distract the patient's necessary fixation of the optical axis with the sound or sight of the movement for positioning the light spot from the projector.
The Goldman-type tester also has a pen recorder associated with the handle end of the pantograph-like arms for recording the spot positions the patient can or cannot see. The light spot is progressed along a radial meridian toward or away from the fixated visual axis until, for example, the patient cannot see it. This procedure is repeated along sufficient meridians to define successive points at the ends of the meridian lines recorded by the pen at which the patient has equal visual limits. These points can then be connected graphically by a line called an isopter which displays the field of the patient's vision under the test conditions. The pen recording from the test device must, therefore, be further processed graphically to achieve the desired isopter plot.
The manual operation of the pantograph-like arms, the constructional complexity of the arm arrangement, the patient distraction in sound or sight from fixing the visual axis at the fixation target from the movement of the mechanical arms adjacent the patient for variably positioning the testing light spot, and the need to further manually process the pen recording of the patient's visual ability to develop the desired isopters all tend to limit the desirability of Goldman-type visual field testers. A way of precisely and automatically projecting a light beam which is visually and audibly less distracting and which, from the automatic positioning control, could also automatically develop isopters would thus be desirable.